Patent Document 1 describes a three-dimensional motor according to an invention by the present inventor. The three-dimensional motor is provided with a stator with windings disposed about axes in three directions orthogonal to one another for producing respective rotating fields such that a composite rotating field of an arbitrary direction can be produced; and a rotor supported within the stator such that the rotor can be rotated in an arbitrary direction and rotated by the rotating fields of the stator. The three-dimensional motor may provide a three-dimensional synchronous motor when a permanent magnet is used for the rotor, a three-dimensional induction motor when a material allowing induction current flow is used for the rotor, or a three-dimensional reluctance motor when a magnetic material with salient poles is used for the rotor.
Patent Document 2 describes a spherical stepping motor according to an invention by the present inventor. The spherical stepping motor includes a rotor with permanent magnets disposed at the vertexes and the center of each face of a polyhedron inscribed in the rotor, and a stator with electromagnets disposed at the vertexes and the center of each face of a polyhedron inscribed in the stator, the number of corners of a polygon of the polyhedron inscribed in the rotor and the number of corners of a polygon of the polyhedron inscribed in the stator being coprime. The combination of the permanent magnets of the rotor and the electromagnets of the stator may be selected from a configuration in which the electromagnets are disposed on the rotor side while the electromagnets are disposed on the stator side; a configuration in which a magnetic material is disposed on the rotor side while the electromagnets are disposed on the stator side; a configuration in which the permanent magnets are disposed on the rotor side while a hybrid configuration of the permanent magnets and the electromagnets is disposed on the stator side; or a configuration in which a hybrid configuration of the permanent magnets and the electromagnets is disposed on the rotor side while a hybrid configuration of the permanent magnets and the electromagnets is disposed on the stator side.
Patent Document 3 describes a spherical stepping motor and a spherical AC servo motor according to an invention by the present inventor. The spherical stepping motor includes a rotor with permanent magnets disposed at the vertexes, the center of the sides, and the center of each face of a polyhedron inscribed in the rotor, and a stator with electromagnets disposed at the vertexes and the center of each face of a polyhedron inscribed in the stator, the number of corners of a polygon of the polyhedron inscribed in the rotor and the number of corners of a polygon of the polyhedron inscribed in the stator being coprime. A spherical AC servo motor may be configured by adopting a Halbach array for the permanent magnets of the rotor and supplying a sine wave current to the electromagnets.
Non-patent Document 1 describes a spherical synchronous motor with a configuration similar to the configuration of the three-dimensional motor described in Patent Document 1.
Non-patent Documents 2 and 3 describe spherical induction motors. The spherical induction motors described in these documents rotate with the same principle as that for the three-dimensional motor described in Patent Document 1. The spherical induction motor described in Non-patent Document 2 differs from the three-dimensional motor described in Patent Document 1 in that the windings in Non-patent Document 2 are multipolarized.
Non-patent Document 4 describes a spherical reluctance motor. The spherical reluctance motor produces a rotating field by a total of 20 electromagnets circumferentially disposed in upper and lower two levels on a stator, and produces a rotating force by utilizing a change in reluctance with respect to salient poles circumferentially disposed in upper and lower two levels on a rotor.
Non-patent Document 5 describes a spherical stepping motor. The spherical stepping motor includes a stator with a total of 16 electromagnets; specifically, one at the center of a bottom surface, five on a circumference around the center, and further 10 on an outer circumference around the center. The spherical stepping motor also includes a rotor with a total of 24 permanent magnets; specifically, 4, 8, and 12 permanent magnets on respective circumferences around the center of the bottom surface. The rotor is rotated by attracting the magnets of the rotor by supplying a current to the electromagnets near where the rotor is desired to be moved.
Non-patent Document 6 describes a spherical stepping motor with a configuration different from that of the spherical stepping motor according to Non-patent Document 5. The spherical stepping motor according to Non-patent Document 6 includes a spherical rotor and stator which are each segmented along longitudes and latitudes. The rotor includes permanent magnets with N-poles and S-poles facing the surface alternately arranged in the segments. The stator includes electromagnets arranged in the corresponding segments. The rotor includes 4 stages of 12 poles for a total of 48-pole permanent magnets. The stator includes 6 stages of 16 poles per stage for a total of 96 electromagnets.
Patent Document 1: JP 6-85630 A
Patent Document 2: JP 2008-92758 A
Patent Document 3: JP 2009-77463 A
Non-patent Document 1: J. Wang; K. Mitchell; G. W. Jewell; D. Howe: Multi-Degree-of-Freedom Spherical permanent Magnet Motors, Proc. ICRA2001 pp. 1798-1805, 2001
Non-patent Document 2: Bruno Dehez; Damien Grenier; Benoit Raucent: Two-Degree-of Freedom Spherical Actuator for Omnimobile ROBOT. Proc. 2002 IEEE International Conference on Robotics and Automation, pp. 2381-2386, 2002
Non-patent Document 3: A. Tanaka, M. Watada, S. Toril and D. Ebihara, “Proposal and Design of Multi-Degree-of-Freedom Spherical Actuator”, Proc. of the 11th MAGDA Conference, pp. 169-172, 2002
Non-patent Document 4: K. M. Lee, H. Son, J. Joni: Concept Development and Design of a Spherical Wheel Motor (SWM). IEEE Transactions on Proceedings of the 2005 IEEE Int. Conf. Robotics and Automation, pp. 3663-3668, 2005
Non-patent Document 5: David Stein; Gregory S. Chirikjian: Experiments in the Communication and Motion Planning of a Spherical Stepper Motor. ASME paper DETOO/MECH-14115, pp.1-7, 2000
Non-patent Document 6: K. Kahlen; R. W. De Doncker: Current regulators for multiple-phase permanent magnet spherical machines. Proc. 2000 IEEE Industrial Application, pp.2011-2015, 2000
In the three-dimensional motor according to Patent Document 1, when an opening portion is increased for increasing the range of movement of the output axis, it may become impossible to dispose the windings for producing the rotating fields a bout the respective axes in the three orthogonal directions. This problem may be overcome by disposing the windings about the axes in the three directions inclined by approximately 10° from each plane in a three-dimensional space. However, in this case, the rotating field about a vertical axis may become the strongest, with the rotating field decreasing and becoming more unstable with increasing angle of inclination of the rotation axis of the output axis. Further, because the rotor is rotated by tracking the rotating field, it is difficult to keep the rotor stationary in the three-dimensional space. In addition, the three-dimensional motor needs to maintain the magnetic flux in a state close to a sine wave distribution when current flows through the windings, and this need needs to be somehow addressed.
In the spherical synchronous motor according to Non-patent Document 2, the winding in the output axis direction among the windings for producing the rotating fields about the respective axes in the three orthogonal directions is lacking for providing the output axis. Thus, as the rotation axis is inclined from the central axis in the opening, the rotating force sharply declines and becomes unstable. Further, the spherical synchronous motor is difficult to keep stationary, as in the case of the three-dimensional motor according to Patent Document 1. In addition, because the spherical induction motor is multipolarized, the produced torque may be smaller than that of the three-dimensional motor according to Patent Document 1.
In the spherical induction motor according to Non-patent Document 3, a large part of the winding is lacking due to the provision of an opening, so that it is difficult to uniformly compose rotating fields in a direction greatly inclined from the opening central axis. In the spherical induction motors according to Non-patent Documents 2 and 3, slipping is caused because they are both induction motors, so that positioning of the rotor is difficult.
In the spherical reluctance motor according to Non-patent Document 4, the rotation axis of the rotor as it rotates can be inclined only within the range of ±5° for structural reasons.
In the spherical stepping motor according to Non-patent Document 5, both the electromagnets and the permanent magnets of the rotor are disposed on circumferences about the center of the bottom surface. Thus, while rotation about the center of the bottom surface can be made by regularly determining the electromagnets through which current is to be passed, it is very difficult to determine the electromagnets for rotating the rotor in other directions. The more the center of the bottom surface of the rotor is displaced from the center of the bottom surface of the stator, the more difficult it becomes to rotate the rotor. This is due to the structure in which both the electromagnets and the permanent magnets are disposed concentrically about the center of the bottom surface.
In the spherical stepping motor according to Non-patent Document 6, when the rotor is rotated about the vertical axis, the rotation can be controlled in the same way as for a stepping motor with a 12-pole rotor and a 16-pole stator on a planar surface. However, when the axis is inclined, the control becomes suddenly difficult. This is due to the fact that it is very difficult to determine the currents to be supplied to the 96 electromagnets by a parallel computation process using a DSP board.
In all of the motors according to Patent Document 1 and Non-patent Documents 2 to 6, control of the rotation about the opening central axis may be considered an extension of conventional motor control technology. However, as the direction of the axis is displaced from the opening central axis, control becomes increasingly difficult or impossible. This is due to the fact that the motor structure does not have spherical symmetry.
The above problems may be overcome by the spherical stepping motor described in Patent Document 2. In the spherical stepping motor, strong drive force can be obtained even when the direction of the rotation axis of the rotor is displaced from the opening center of the stator, rotation control is easy, and large drive force can be obtained by increasing the lines of magnetic force that flow into and out of the magnetic path between the permanent magnets of the rotor and the electromagnets of the stator.
However, in the spherical stepping motor according to Patent Document 2, when the permanent magnets are arranged on the rotor, the permanent magnets disposed at the vertexes of the polyhedron have the same polarity. Thus, even when the magnetic path is formed by reversing the polarity of the permanent magnet disposed at the center of each face of the polyhedron, the magnetic path is concentrated at the permanent magnet positioned at the center of each face of the polyhedron. As a result, magnetic saturation may be caused and the output may be limited.
The above problem may be overcome by the spherical stepping motor and the spherical AC servo motor described in Patent Document 3. By adopting a polyhedron such that the number of the corners of each face is an even number (regular hexahedron or truncated octahedron) as the polyhedron inscribed in the rotor, the permanent magnets disposed on the rotor can be arranged such that all of the N-poles and S-poles are adjacent to one another. Thus, the spherical stepping motor and the spherical AC servo motor can be configured such that magnetic saturation can be avoided.
However, in the spherical stepping motor and the spherical AC servo motor according to Patent Document 3, because the polyhedron inscribed in the rotor is limited to the polyhedron such that the number of corners of each face is an even number, the structure of the rotor is strictly limited. Further, in Patent Documents 2 and 3, the number of corners of the polyhedron inscribed in the rotor and the number of corners of the polyhedron inscribed in the stator need to be coprime. Thus, the rotor and the stator are strictly limited structurally. Further, the rotation axis of the rotor and the rotation axis of the stator need to be aligned before the rotor is rotated, so that the corresponding structure and control need to be added.
In view of the above problems, an object of the present invention is to provide means such that the selection of the polyhedron inscribed in the rotor and the stator can be made more freely, so that the degree of freedom in designing the spherical stepping motor and the spherical AC servo motor can be significantly increased.